In bore drilling (including extended reach (horizontal drilling) applications) there is often a need to provide a drilling apparatus with a drill string (whether jointed drill rods, or continuous coil tube) containing a vibratory device that provides a level of axial excitation to minimise the frictional forces, which can dramatically slow or stop a drilling or re-entry operation. In addition, such a vibratory device can be beneficial to help free drill strings once they have become stuck.
Often such vibratory devices are difficult to manufacture.